Electroless process for treating metallic surfaces and products formed thereby

ABSTRACT

The disclosure relates to a process for forming a deposit on the surface of a metallic or conductive surface. The process employs an electroless process to deposit a silicate containing coating or film upon a metallic or conductive surface.

[0001] The subject matter herein claims benefit of previously filed U.S.patent application Ser. No. 60/381,024, filed on May 15, 2002 and U.S.patent application Ser. No. 60/310,007, filed on Aug. 03 2002, bothentitled “An Electroless Process For Treating Metallic Surfaces AndProduct Formed Thereby”; the disclosure of both is hereby incorporatedby reference.

FIELD OF THE INVENTION

[0002] The instant invention relates to a process for forming a depositon the surface of a metallic or conductive surface. The process employsa process to deposit, for example, a mineral containing coating or filmupon a metallic, metal containing or an electrically conductive surface.

BACKGROUND OF THE INVENTION

[0003] Silicates have been used in electrocleaning operations to cleansteel, tin, among other surfaces. Electrocleaning is typically employedas a cleaning step prior to an electroplating operation. Usage ofsilicates as cleaners is described in “Silicates As Cleaners In TheProduction of Tinplate” is described by L. J. Brown in February 1966edition of Plating; European Patent No. 00536832/EP B1(Metallgesellschaft A G); U.S. Pat. Nos. 5,902,415, 5,352,296 and4,492,616.

[0004] Processes for electrolytically forming a protective layer or filmby using an anodic method are disclosed by U.S. Pat. No. 3,658,662(Casson, Jr. et al.), and United Kingdom Patent No. 498,485.

[0005] U.S. Pat. No. 5,352,342 to Riffe, which issued on Oct. 4, 1994and is entitled “Method And Apparatus For Preventing Corrosion Of MetalStructures” that describes using electromotive forces upon a zincsolvent containing paint; hereby incorporated by reference. U.S. Pat.Nos. 5,700,523, and 5,451,431; and German Patent No. 93115628 describesa processes for using alkaline metasilicates to treat metallic surfaces.

[0006] The disclosure of the previously identified patents andpublications is hereby incorporated by reference.

SUMMARY OF THE INVENTION

[0007] The instant invention solves problems associated withconventional practices by providing an electroless process for treatingmetallic surfaces. By “electroless” it is meant that no current isapplied from an external source (a current may be generated in-situ dueto an interaction between the metallic surface and the medium). Theprocess employs a silicate medium having a controlled and predeterminedsilicate concentration, temperature and pH. As a result, the silicatemedium that interacts with the metallic surface to form surface havingone or more improved properties. The inventive process controls themedium's characteristics and the surrounding environment in order toobtain a desired film or layer upon the metal surface, e.g, a film orlayer having low surface porosity or high density. The characteristicsof the film or layer can be controlled or modified by varying thetemperature, pH, lattice builders (i.e., medium dopants), rate offormation, heat, pressure, pre and post treatments and silicateconcentration.

[0008] The inventive process can form a surface comprising a minerallayer comprising an amorphous matrix surrounding or incorporating metalsilicate crystals upon the substrate. The characteristics of the minerallayer are described in greater detail in the copending and commonlyassigned patent applications listed below.

[0009] A metallic surface that is treated (e.g., forming the minerallayer) by the inventive process can possess improved corrosionresistance, increased electrical resistance, heat resistance,flexibility, resistance to stress crack corrosion, adhesion to topcoats,among other properties. The improved heat resistance broadens the rangeof processes that can be performed subsequent to forming the inventivelayer, e.g., heat cured topcoatings, stamping/shaping, riveting, amongother processes. The treated surface also imparts greater corrosionresistance (e.g., ASTM B-117), among other beneficial properties, thanconventional tri-valent or hexa-valent chromate systems. The inventiveprocess can provide a zinc-plate article having an ASTM B-117 resistanceto white rust of at least about 96 hours (and normally greater thanabout 150 hours), and resistance to red rust of at least about 250 (andnormally greater than about 400 hours). The corrosion resistance can beimproved by adding a dopant to the silicate medium, using a rinse and/orapplying at least one sealer/topcoating.

[0010] The inventive process is a marked improvement over conventionalmethods by obviating the need for solvents or solvent containing systemsto form a corrosion resistant layer, e.g., a mineral layer. In contrast,to conventional methods the inventive process can be substantiallysolvent free. By “substantially solvent free” it is meant that less thanabout 5 wt. %, and normally less than about 1 wt. % volatile organiccompounds (V.O.C.s) are present in the electrolytic environment.

[0011] The inventive process is also a marked improvement overconventional methods by reducing, if not eliminating, chromate and/orphosphate containing compounds (and issues attendant with using thesecompounds such as waste disposal, worker exposure, among otherundesirable environmental impacts). While the inventive process can beemployed to enhance chromated or phosphated surfaces, the inventiveprocess can replace these surfaces with a more environmentally desirablesurface. The inventive process, therefore, can be “substantiallychromate free” and “substantially phosphate free” and in turn producearticles that are also substantially chromate (hexavalent and trivalent)free and substantially phosphate free. The inventive process can also besubstantially free of heavy metals such as chromium, lead, cadmium,barium, among others. By substantially chromate free, substantiallyphosphate free and substantially heavy metal free it is meant that lessthan 5 wt. % and normally about 0 wt. % chromates, phosphates and/orheavy metals are present in a process for producing an article or theresultant article.

CROSS REFERENCE TO RELATED PATENTS AND PATENT APPLICATIONS

[0012] The subject matter of the instant invention is related tocopending and commonly assigned WIPO Patent Application Publication No.WO 98/33960, Non-Provisional U.S. patent application Ser. Nos.09/814,641; 08/850,323 (Now U.S. Pat. No. 6,165,257); 08/850,586 (NowU.S. Pat. No. 6,143,420); and 09/016,853 (now allowed), filedrespectively on May 2, 1997 and Jan. 30 1998, and 08/791,337 (now U.S.Pat. No. 5,938,976), filed on Jan. 31, 1997, in the names of Robert L.Heimann et al., as a continuation in part of Ser. No. 08/634,215 (filedon Apr. 18, 1996) in the names of Robert L. Heimann et al., and entitled“Corrosion Resistant Buffer System for Metal Products”, which is acontinuation in part of Non-Provisional U.S. patent application Ser. No.08/476,271 (filed on Jun. 7 1995) in the names of Heimann et al., andcorresponding to WIPO Patent Application Publication No. WO 96/12770,which in turn is a continuation in part of Non-Provisional U.S. patentapplication Ser. No. 08/327,438 (filed on Oct. 21, 1994), now U.S. Pat.No. 5,714,093.

[0013] The subject matter of this invention is related toNon-Provisional patent application Ser. No. 09/016,849 (Attorney DocketNo. EL004RH-1), filed on Jan. 30, 1998 and entitled “CorrosionProtective Coatings”. The subject matter of this invention is alsorelated to Non-Provisional patent application Ser. No. 09/016,462(Attorney Docket No. EL005NM-1), filed on Jan. 30, 1998 and entitled“Aqueous Gel Compositions and Use Thereof” (now U.S. Pat. No.6,033,495).

[0014] The subject matter of this invention is also related toNon-Provisional patent application Ser. No. 09/814,641 (Attorney DocketNo. EL008RH-6), filed on Mar. 22, 2001, and entitled “An Energy EnhancedProcess For Treating A Conductive Surface And Products Formed Thereby”(and corresponds to PCT patent application Ser. No. PCT/US01/09293), andNon-Provisional patent application Ser. No. ______ (Attorney Docket No.EL023RH-1), filed on Aug. 03, 2002 and entitled “An Electrolytic AndElectroless Process For Treating Metallic Surfaces And Products FormedThereby”, and Ser. No. ______ (Attorney Docket No. EL022RH-1), filed onAug. 03, 2002 and entitled “Process For Treating A Conductive SurfaceAnd Products Formed Thereby”.

[0015] The disclosure of the previously identified patents, patentapplications and publications is hereby incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 illustrates the open-circuit potential of galvanized steelpanels immersed in the inventive medium having a pH 10.5.

[0017]FIG. 2 illustrates the open-circuit potential of galvanized steelpanels immersed in the inventive medium having a pH 11.

[0018]FIG. 3 illustrates the open-circuit potential of galvanized steelpanels immersed in the inventive medium having a pH of 11.5.

[0019]FIG. 4 illustrates the open-circuit potential of galvanized steelpanels immersed in the inventive medium having a pH 12.

[0020]FIG. 5 illustrates the corrosion potentials of galvanized steelpanels immersed in the inventive medium having a temperature of 75 C andpHs of 10.5, 11, 11.5 and 12.

[0021]FIG. 6 illustrates the corrosion potentials of galvanized steelpanesl immersed in the inventive medium having a temperature of 80 C andpHs of 10.5, 11, 11.5 and 12.

[0022]FIG. 7 illustrates the open circuit potential for galvanized steelpanels exposed to pHs of 10.5, 11 and 12.

[0023]FIG. 8 illustrates a comparison of the SEM and EDAX analysis ofsamples exposed to the inventive medium and rinsed immediately andrinsed after 24 hours.

[0024]FIG. 9 illustrates a comparison of increasing amounts of sodiumborohydride addition to the inventive medium.

[0025]FIG. 10 illustrates a comparison of corrosion resistance ofsamples treated with the inventive medium with sodium borohydrideaddition.

[0026]FIG. 11 illustrates a comparison of corrosion resistance ofsamples treated with the inventive medium with sodium borohydrideaddition and a thermal post-treatment.

[0027]FIG. 12 illustrates a voltagrams for samples treated in theinventive medium with sodium borohydride addition.

[0028]FIG. 13 illustrates inhibiting efficiencies based upon thevoltagrams of FIG. 12.

[0029]FIG. 14 illustrates a voltagrams for samples treated in theinventive medium with sodium borohydride addition and a thermalpost-treatment.

[0030]FIG. 15 illustrates inhibiting efficiencies based upon thevoltagrams of FIG. 14.

[0031]FIG. 16 illustrates cyclic voltagrams for samples treated in theinventive medium with sodium borohydride addition.

[0032]FIG. 17 illustrates inhibiting efficiencies based upon thevoltagrams of FIG. 16.

[0033]FIG. 18 illustrates the affect on inhibiting efficiencies on airdried samples after immersion in water for one week.

[0034]FIG. 19 illustrates the affect on inhibiting efficiencies onsamples having a thermal post-treatment after immersion in water for oneweek.

[0035]FIG. 20 illustrates an SEM image of samples treated with theinventive medium with sodium borohydride addition before and afterimmersion in water.

[0036]FIG. 21 illustrates an EDAX of samples treated with the inventivemedium with sodium borohydride addition.

[0037]FIG. 22 illustrates an EDAX of samples treated with the inventivemedium with sodium borohydride addition and a thermal post treatment.

DETAILED DESCRIPTION

[0038] The instant invention relates to a process for depositing orforming a beneficial surface (e.g., a mineral containing coating orfilm) upon a metallic surface. The process contacts at least a portionof a metal surface with a silicate medium, e.g., containing solublemineral components or precursors thereof, having controlled andpredetermined silicate concentration, temperature and pH. By “mineralcontaining coating”, “mineralized film” or “mineral” it is meant torefer to a relatively thin coating or film which is formed upon a metalsurface wherein at least a portion of the coating or film comprises atleast one metal containing mineral, e.g., an amorphous phase or matrixsurrounding or incorporating crystals comprising a zinc disilicate.Mineral and Mineral Containing are defined in the previously identifiedCross Reference To Related Patents and Paten Applications; incorporatedby reference.

[0039] By “metal containing”, “metal”, or “metallic”, it is meant torefer to sheets, shaped articles, fibers, rods, particles, continuouslengths such as coil and wire, metallized surfaces, among otherconfigurations that are based upon at least one metal and alloysincluding a metal having a naturally occurring, or chemically,mechanically or thermally modified surface. Typically a naturallyoccurring surface upon a metal will comprise a thin film or layercomprising at least one oxide, hydroxides, carbonates, sulfates,chlorides, among others. The naturally occurring surface can be removedor modified by using the inventive process.

[0040] The metal surface refers to a metal article or body as well as anon-metallic member having an adhered metal or conductive layer. Whileany suitable surface can be treated by the inventive process, examplesof suitable metal surfaces comprise at least one member selected fromthe group consisting of galvanized surfaces, sheradized surfaces, zinc,iron, steel, brass, copper, nickel, tin, aluminum, lead, cadmium,magnesium, alloys thereof such as zinc-nickel alloys, tin-zinc alloys,zinc-cobalt alloys, zinc-iron alloys, among others. If desired, themineral layer can be formed on a non-conductive substrate having atleast one surface coated with a metal, e.g., a metallized polymericarticle or sheet, ceramic materials coated or encapsulated within ametal, among others. Examples of metallized polymer comprise at leastone member selected from the group of polycarbonate, acrylonitrilebutadiene styrene (ABS), rubber, silicone, phenolic, nylon, PVC,polyimide, melamine, polyethylene, polyproplyene, acrylic, fluorocarbon,polysuilfone, polyphenyene, polyacetate, polystyrene, epoxy, amongothers. Conductive surfaces can also include carbon or graphite as wellas conductive polymers (polyaniline for example).

[0041] The metal surface can possess a wide range of sizes andconfigurations, e.g., fibers, coils, sheets including perforatedacoustic panels, chopped wires, drawn wires or wire strand/rope, rods,couplers (e.g., hydraulic hose couplings), fibers, particles, fasteners(including industrial and residential hardware), brackets, nuts, bolts,rivets, washers, cooling fins, stamped articles, powdered metalarticles, among others. The limiting characteristic of the inventiveprocess to treat a metal surface is dependent upon the ability of thesurface to be contacted with the inventive silicate medium.

[0042] The inventive process can be operated on a batch or continuousbasis. The type of process will depend upon the configuration of themetal being treated. The contact time within the silicate medium rangesfrom about 10 seconds to about 50 minutes and normally about 1 to about15 minutes. The inventive process can be practiced in any suitableapparatus. Examples of suitable apparatus comprise a batch processperformed in polyproplyene tanks having means for circulating thesilicate medium and maintaining a predetermined temperature.

[0043] The silicate containing medium can be a fluid bath, gel, spray,fluidized beds, among other methods for contacting the substrate withthe silicate medium. Examples of the silicate medium comprise a bathcontaining at least one silicate, a gel comprising at least one silicateand a thickener, among others. The medium can comprise a bath comprisingat least one of potassium silicate, calcium silicate, lithium silicate,sodium silicate, ammonium silicate, compounds releasing silicatemoieties or species, among other silicates. The bath can comprise anysuitable polar or non-polar carrier such as water, alcohol, ethers,carboxillic acids, among others. Normally, the bath comprises at leastone water-soluble silicate such as sodium silicate and de-ionized waterand optionally at least one dopant (e.g. chlorides among othermonovalent species). Typically, the at least one dopant is water solubleor dispersible within an aqueous medium.

[0044] The silicate containing medium typically has a basic pH.Normally, the pH will range from greater than about 9 to about 13 andtypically, about 10 to about 12. The pH of the medium can be monitoredand maintained by using conventional detection and delivery methods. Theselected detection method should be reliable at relatively high sodiumconcentrations and under ambient conditions.

[0045] The silicate medium is normally aqueous and can comprise at leastone water soluble or dispersible silicate in an amount from greater thanabout 0 to about 40 wt. %, usually, about 1 to 15 wt. % and typicallyabout 3 to 8 wt. %. The amount of silicate in the medium should beadjusted to accommodate silicate sources having differing concentrationsof silicate. The silicate containing medium is also normallysubstantially free of heavy metals, chromates and/or phosphates.

[0046] The silicate medium can be modified by adding at least onestabilizing compound (e.g., stabilizing by complexing metals). Anexample of a suitable stabilizing compound comprises phosphines, sodiumcitrate, ammonium citrate, ammonium iron citrate, sodium salts ofethylene diamine tetraacetic acid (EDTA) and nitrilotriacetic acid(NTA), 8-hydroxylquinoline, 1,2-diaminocyclohexane-tetracetyic acid,diethylene-triamine pentacetic acid, ethylenediamine tetraacetic acid,ethylene glycol bisaminoethyl ether tetraacetic acid, ethyl etherdiaminetetraacetic acid, N′-hydroxyethylethylenediamine triacetic acid,1-methyl ethylene diamine tetraacetic acid, nitriloacetic acid,pentaethylene hexamine, tetraethylene pentamine, triethylene tetraamine,among others.

[0047] In one aspect, the silicate medium has a basic pH and comprisesat least one water soluble silicate, water and colloidal silica. Thesilicate medium can also be modified by adding colloidal particles suchas colloidal silica (commercially available as Ludox® AM-30, HS-40,among others). The colloidal silica has a particle size ranging fromabout 10 nm to about 50 nm. The size of particles in the medium rangesfrom about 10 nm to 1 micron and typically about 0.05 to about 0.2micron. The medium has a turbidity of about 10 to about 700, typicallyabout 50 to about 300 Nephelometric Turbidity Units (NTU) (as determinedin accordance with conventional procedures).

[0048] The temperature of the silicate medium can be controlled tooptimize the interaction between the medium and a metal surface.Normally, the temperature will range from about 50 to at least about 100C and typically about 50 to 100 C (e.g., 55 C). This temperature can bemaintained by using conventional heaters and related control systems. Ifdesired, the metal surface can be heated prior to being introduced intothe medium.

[0049] The chemical and/or physical properties of the silicate mediumcan be affected by exposing the medium to a source of electrical ormagnetic energy. For example, the bath can be exposed to a source ofenergy such as the electrical current described in aforementioned U.S.Ser. No. 09/814,641; hereby incorporated by reference. Such exposure canimprove the interaction between the medium and the metal surface,partially polymerize the silicate medium, partially crystallize thesilicate medium, among other affects.

[0050] The silicate medium can be modified by adding water/polar carrierdispersible or soluble polymers. If utilized, the amount of polymer orwater dispersible materials normally ranges from about 0 wt. % to about10 wt. %. Examples of polymers or water dispersible materials that canbe employed in the silicate medium comprise at least one member selectedfrom the group of acrylic copolymers (supplied commercially asCarbopol®, zirconyl ammonium carbonate, hydroxyethyl cellulose, clayssuch as bentonite, fumed silica, solutions comprising sodium silicate(supplied commercially by MacDermid as JS2030S), among others. Asuitable composition can be obtained in an aqueous compositioncomprising about 3 wt. % silicate (obtained from N-grade Sodium SilicateSolution (PQ Corp) that comprises 25% silicate), optionally about 0.5wt. % Carbopol EZ-2 (BF Goodrich), about 5 to about 10 wt. % fumedsilica, mixtures thereof, among others.

[0051] In an aspect of the invention, the silicate medium is modified toinclude at least one dopant material. The dopants can be useful forbuilding additional thickness of the deposited layer, hydroxides ofiron, aluminum, manganise, and magnesium among others. The amount ofdopant can vary depending upon the properties of the dopant and desiredresults. Typically, the amount of dopant will range from about 0.001 wt.% to about 5 wt. % of the medium (or greater so long as the depositionrate is not adversely affected). Examples of suitable dopants compriseat least one member selected from the group of water dispersible orsoluble salts, oxides and precursors of tungsten, molybdenum (e.g.,molybdenum chloride), titanium (titatantes), zircon, vanadium,phosphorus, aluminum (e.g., aluminates, aluminum chloride, etc), iron(e.g., iron chloride), boron (borates), bismuth, cobalt (e.g., cobaltchloride, cobalt oxide, etc.), gallium, tellurium, germanium, antimony,niobium (also known as columbium), magnesium and manganese, nickel(e.g., nickel chloride, nickel oxide, etc.), sulfur, zirconium(zirconates) mixtures thereof, among others, and usually, salts andoxides of aluminum and iron, and hydroxides of iron, aluminum, manganeseand magnesium, among others; and other water soluble or dispersiblemonovalent species. The dopant can comprise at least one of molybdenicacid, fluorotitanic acid and salts thereof such as titaniumhydrofluoride, ammonium fluorotitanate, ammonium fluorosilicate andsodium fluorotitanate; fluorozirconic acid and salts thereof such asH₂ZrF₆, (NH₄)₂ZrF₆ and Na₂ZrF₆; among others. Alternatively, dopants cancomprise at least one substantially water insoluble material such aselectropheritic transportable polymers, PTFE, boron nitride, siliconcarbide, silicon nitride, aluminum nitride, titanium carbide, diamond,titanium diboride, tungsten carbide, silica (e.g., colloidal silicaavailable commercially as Ludox® AM and HS) metal oxides such as ceriumoxide, powdered metals and metallic precursors such as zinc, amongothers.

[0052] If desired, the dopant can be dissolved or dispersed withoutanother medium prior to introduction into the silicate medium. Forexample, at least one dopant can be combined with a basic compound,e.g., sodium hydroxide, and then added to the silicate medium. Examplesof dopants that can be combined with another medium comprise zirconia,cobalt oxide, nickel oxide, molybdenum oxide, titanium (IV) oxide,niobium (V) oxide, magnesia, zirconium silicate, alumina, antimonyoxide, zinc oxide, zinc powder, aluminum powder, among others.

[0053] The aforementioned dopants that can be employed for enhancingmineral layer formation rate, modifying the chemistry and/or physicalproperties of the resultant layer, as a diluent for the silicatecontaining medium, among others. Examples of such dopants are iron salts(ferrous chloride, sulfate, nitrate), aluminum fluoride, fluorosilicates(e.g., K2SiF6), fluoroaluminates (e.g., potassium fluoroaluminate suchas K2AlF5-H2O), mixtures thereof, among other sources of metals andhalogens. The dopant materials can be introduced to the metal surface inpretreatment steps, in post treatment steps (e.g., rinse), and/or byalternating exposing the metal surface to solutions of dopants andsolutions of silicates if the silicates will not form a stable solutionwith the dopants, e.g., one or more wafer soluble dopants. The presenceof dopants in the silicate medium can be employed to form tailoredsurfaces upon the metal, e.g., an aqueous sodium silicate solutioncontaining aluminate can be employed to form a layer comprising oxidesof silicon and aluminum. That is, at least one dopant (e.g., zinc) canbe co-deposited along with at least one siliceous species (e.g., amineral) upon the substrate.

[0054] The silicate medium can also be modified by adding at least onediluent. Examples of suitable diluent comprise at least one memberselected from the group of sodium sulphate, surfactants, de-foamers,colorants/dyes, conductivity modifiers, among others. The diluent (e.g.,sodium sulfate) can be employed for reducing the affects of contaminantsentering the silicate medium, reducing bath foam, among others. When thediluent is employed as a defoamer, the amount normally comprises lessthan about 5 wt. % of the medium, e.g., about 1 to about 2 wt. %.

[0055] According to one embodiment of the invention, the silicate mediumfurther comprises at least one reducing agent. An example of a suitablereducing agent comprises sodium borohydride, phosphorus compounds suchas hypophosphide compounds, phosphate compounds, among others. Withoutwishing to be bound by any theory or explanation, it is believed thatthe reducing agent may reduce water present in the silicate mediumthereby modifying the surface pH of articles that contact the silicatemedium (e.g., article may induce or catalyze activity of the reducingagent). According to one embodiment, the concentration of sodiumborohydride is typically 1 gram per liter of bath solution to about 20grams per liter of bath solution more typically 5 grams per liter ofbath solution to about 15 gram per liter of bath solution. In oneillustrative and preferred embodiment, 10 grams of sodium borohydrideper liter of bath solution is utilized. When employed the reducingagent, can cause hydrogen evolution once the bath/medium has beensufficiently heated.

[0056] Contact with the inventive silicate medium can be preceded byand/or followed with conventional pre-treatments and/or post-treatmentsknown in this art such as cleaning or rinsing, e.g., immersion/spraywithin the treatment, sonic cleaning, double counter-current cascadingflow; alkali or acid treatments, among other treatments. By employing asuitable post-treatment the solubility, corrosion resistance (e.g.,reduced white rust formation when treating zinc containing surfaces),sealer and/or topcoat adhesion, among other properties of surface of thesubstrate formed by the inventive method can be improved. If desired,the post-treated surface can be sealed, rinsed and/or topcoated, e.g.,silane, epoxy, latex, fluoropolymer, acrylic, titanates, zirconates,carbonates, urethanes, among other coatings.

[0057] In one aspect of the invention, a pre-treatment comprisesexposing the substrate to be treated to at least one of an acid, base(e.g., zincate solution), oxidizer, among other compounds. Thepre-treatment can be employed for cleaning oils, removing excess oxidesor scale, equipotentialize the surface for subsequent mineralizationtreatments, convert the surface into a mineral precursor, functionalizethe surface (e.g., a hydroxilized surface), among other benefits.Conventional methods for acid cleaning metal surfaces are described inASM, Vol. 5, Surface Engineering (1994), and U.S. Pat. No. 6,096,650;hereby incorporated by reference.

[0058] In one aspect of the invention, the metal surface is pre-treatedor cleaned electrolytically by being exposed to an anodic environment.That is, the metal surface is exposed to the silicate medium wherein themetal surface is the anode and a current is introduced into the medium.By using the metal as the anode in a DC cell and maintaining a currentof about 10A/ft2 to about 150A/ft2, the process can generate oxygen gas.The oxygen gas agitates the surface of the workpiece while oxidizing thesubstrate's surface. The surface can also be agitated mechanically byusing conventional vibrating equipment. If desired, the amount of oxygenor other gas present during formation of the mineral layer can beincreased by physically introducing such gas, e.g., bubbling, pumping,among other means for adding gases.

[0059] If desired, the inventive method can include a thermalpost-treatment. The metal surface can be removed from the silicatemedium, dried (e.g., at about 100 to 150 C for about 2.5 to 10 minutes),rinsed in deionized water and then dried in order to remove rinse water.This is in contrast to conventional metal treatments that rinse(s) andthen dry. The dried surface may be processed further as desired; e.g.contacted with a sealer, rinse or topcoat. If desired, the rinse cancomprise a reactive component such as a silane, carbonate, zirconate,colloidal silica, among other compounds that interact with the treatedmetallic surface.

[0060] In aspect of the invention, the thermal post treatment comprisesheating the surface. Typically the amount of heating is sufficient toconsolidate or densify the inventive surface without adversely affectingthe physical properties of the underlying metal substrate. Heating canoccur under atmospheric conditions, within a nitrogen containingenvironment, among other gases. Alternatively, heating can occur in avacuum. The surface may be heated to any temperature within thestability limits of the surface coating and the surface material.Typically, surfaces are heated from about 75° C. to about 250° C., moretypically from about 150° C. to about 200° C. If desired, the heattreated component can be rinsed in water to remove any residual watersoluble species and then dried again (e.g., at a temperature and timesufficient to remove water).

[0061] If desired, prior to heating the inventive surface can becontacted with a solution containing a material that reacts with thesurface at elevated temperatures, e.g., a eutectic formed between silicaand at least one of Al2O3, B2O3, Fe2O3, MgO, phosphates, among others.Normally, the heating will be sufficient to cause sintering or adesirable interaction without adversely affecting the underlying metal.Alternatively or in addition to heating, the metal surface can beexposed to an atmosphere having controlled pressure in order to tailorthe treated surface.

[0062] In one aspect of the invention, a post treatment comprisesexposing the substrate to a source of at least one carbonate orprecursors thereof. Examples of carbonate comprise at least one memberfrom the group of gaseous carbon dioxide, lithium carbonate, lithiumbicarbonate, sodium carbonate, sodium bicarbonate, potassium carbonate,potassium bicarbonate, rubidium carbonate, rubidium bicarbonate,rubidium acid carbonate, cesium carbonate, ammonium carbonate, ammoniumbicarbonate, ammonium carbamate and ammonium zirconyl carbonate.Normally, the carbonate source will be water soluble. In the case of acarbonate precursor such as carbon dioxide, the precursor can be passedthrough a liquid (including the silicate containing medium) and thesubstrate immersed in the liquid. One specific example of a suitablepostreatment is disclosed in U.S. Pat. No. 2,462,763; herebyincorporated by reference. Another specific example of a post treatmentcomprises exposing a treated surface to a solution obtained by dilutingammonium zirconyl carbonate (1:4) in distilled water (e.g., Bacote® 20supplied by Magnesium Elektron Corp). If desired, this post treatedsurface can be topcoated (e.g., aqueous or water borne topcoats).

[0063] In another aspect of the invention, the post treatment comprisesexposing the substrate to a source comprising at least one acid sourceor precursors thereof. Examples of suitable acid sources comprise atleast one member chosen from the group of phosphoric acid, hydrochloricacid, molybdic acid, silicic acid, acetic acid, citric acid, nitricacid, hydroxyl substituted carboxylic acid, glycolic acid, lactic acid,malic acid, tartaric acid, ammonium hydrogen citrate, ammoniumbifluoride, fluoboric acid, fluorosilicic acid, among other acid sourceseffective at improving at least one property of the treated metalsurface. The pH of the acid post treatment may be modified by employingat least one member selected from the group consisting of ammoniumcitrate dibasic (available commercially as Citrosol® #503 andMultiprep®, fluoride salts such as ammonium bifluoride, fluoboric acid,fluorosilicic acid, among others. The acid post treatment can serve toactivate the surface thereby improving the effectiveness of rinses,sealers and/or topcoatings (e.g., surface activation prior to contactingwith a sealer can improve cohesion between the surface and the sealerthereby improving the corrosion resistance of the treated substrate).Normally, the acid source will be water soluble and employed in amountsof up to about 15 wt. % and typically, about 1 to about 5 wt. % and havea pH of less than about 5.5.

[0064] In another aspect of the invention, the post treatment comprisescontacting a surface treated by the inventive process with a rinse. By“rinse” it is meant that an article or a treated surface is sprayed,dipped, immersed or other wise exposed to the rinse in order to affectthe properties of the treated surface. For example, a surface treated bythe inventive process is immersed in a bath comprising at least onerinse. In some cases, the rinse can interact or react with at least aportion of the treated surface. Further the rinsed surfaced can bemodified by multiple rinses, heating, topcoating, adding dyes,lubricants and waxes, among other processes. Examples of suitablecompounds for use in rinses comprise at least one member selected fromthe group of titanates, titanium chloride, tin chloride, zirconates,zirconium acetate, zirconium oxychloride, fluorides such as calciumfluoride, tin fluoride, titanium fluoride, zirconium fluoride; coppurouscompounds, ammonium fluorosilicate, metal treated silicas (e.g.,Ludox®), combinations comprising colloidal silica, nitrates such asaluminum nitrate; sulphates such as magnesium sulphate, sodium sulphatezinc sulphate, silanes, siloxyanes, siloxyenes, and copper sulphate;lithium compounds such as lithium acetate, lithium bicarbonate, lithiumcitrate, lithium metaborate, lithium vanadate, lithium tungstate, amongothers. The rinse can further comprise at least one organic compoundsuch as vinyl acrylics, fluorosurfactancts, polyethylene wax, TEOS,zirconyl ammonium carbonate, among others. Examples of commerciallyavailable rinses, sealers and topcoats comprise at least one memberselected from the group of Aqualac® (urethane containing aqueoussolution), W86®, W87®, B37®, T01, E10®, B17, B18 among others (a heatcured coating supplied by the Magni® Group), JS2030S (sodium silicatecontaining rinse supplied by MacDermid Incorporated), JS2040I (amolybdenum containing rinse also supplied by MacDermid Incorporated),EnSeal® C-23 (an acrylic based coating supplied by Enthone), EnSeal®C-26, Enthone® C40 (a pigmented coating supplied Enthone), Microseal®,Paraclene® 99 (a chromate containing rinse), EcoTri® (a silicate/polymerrinse), MCI Plus OS (supplied by Metal Coatings International), silanes(e.g., Dow Corning Z-6040, Gelest SIA 0610.0, among others), ammoniumzirconyl carbonate (e.g., Bacote 20), urethanes (e.g., Agate L18), amongothers. One specific rinse comprises water, water dispersible urethane,and at least one silicate, e.g., refer to commonly assigned U.S. Pat.No. 5,871,668; hereby incorporated by reference. While the rinse can beemployed neat, normally the rinse will be dissolved, diluted ordispersed within another medium such as water, organic solvents, amongothers. While the amount of rinse employed depends upon the desiredresults, normally the rinse comprises about 0.1 wt. % to about 50 wt. %of the rinse medium. The rinse can be employed as multiple applicationsand, if desired, heated. The rinse can be employed after a thermaltreatment, e.g., after removing from the silicate medium the part isdried and then rinsed. Moreover, the aforementioned rinses can bemodified by incorporating at least one dopant, e.g. the aforementioneddopants. The dopant can employed for interacting or reacting with thetreated surface. If desired, the dopant can be dispersed in a suitablemedium such as water and employed as a rinse.

[0065] The inventive process can create a flexible surface that cansurvive secondary processes, e.g., metal deformation for riveting,sweging, crimping, among other processes, and continue to providecorrosion protection. Such is in contrast to typical corrosioninhibitors such as chromates that tend to crack when the underlyingsurface is shaped. If desired, the surface formed by the inventiveprocess can be topcoated (e.g, with a heat cured epoxy), prior tosecondary processing. Articles treated in accordance with the inventiveprocess, topcoated and exposed to a secondary process retain theirdesirable corrosion resistance, coating adhesion, componentfunctionality, among properties.

[0066] The inventive process can provide a surface (e.g., mineralcoating) that can enhance the surface characteristics of the metal orconductive surface such as resistance to corrosion, protect carbon(fibers for example) from oxidation, stress crack corrosion (e.g.,stainless steel), hardness, thermal resistance, improve bonding strengthin composite materials, provide dielectric layers, improve corrosionresistance of printed circuit/wiring boards and decorative metalfinishes, and reduce the conductivity of conductive polymer surfacesincluding application in sandwich type materials.

[0067] The mineral coating can also affect the electrical and magneticproperties of the surface. That is, the mineral coating can impartelectrical resistance or insulative properties to the treated surface.By having an electrically non-conductive surface, articles having theinventive layer can reduce, if not eliminate, electro-galvanic corrosionin fixtures wherein current flow is associated with corrosion, e.g.,bridges, pipelines, among other articles.

[0068] Depending upon the intended usage of the workpiece treated by theinventive method, the workpiece can be coated with a secondary coatingor layer. Alternatively, the treated workpiece can be rinsed (asdescribed above) and then coated with a secondary coating or layer.Examples of such secondary coatings or layers comprise one or moremembers of acrylic coatings (e.g., IRILAC®, e-coats, silanes includingthose having amine, acrylic and aliphatic epoxy functional groups,latex, urethane, epoxies, silicones, alkyds, phenoxy resins (powderedand liquid forms), radiation curable coatings (e.g., UV curablecoatings), lacquer, shellac, linseed oil, among others. Secondarycoatings can be solvent or water borne systems. Secondary coatings canalso include corrosion inhibitors, torque tension modifiers, among otheradditives (e.g., a coating comprising urethanes, acrylics, corrosioninhibitor and sodium silicate). The secondary coatings can be applied byusing any suitable conventional method such as immersing, dip-spin,spraying, among other methods. The secondary coatings can be cured byany suitable method such as UV exposure, heating, allowed to dry underambient conditions, among other methods. An example of UV curablecoating is described in U.S. Pat. Nos. 6,174,932 and 6,057,382; herebyincorporated by reference. Normally, the surface formed by the inventiveprocess will be rinsed, e.g., with at least one of deionized water,silane or a carbonate, or subjected to a thermal treatment (e.g.,removal from the silicate bath, dried and then rinsed to remove residualmaterial), prior to applying a topcoat. The secondary coatings can beemployed for imparting a wide range of properties such as improvedcorrosion resistance to the underlying mineral layer, reduce torquetension, a temporary coating for shipping the treated workpiece,decorative finish, static dissipation, electronic shielding, hydrogenand/or atomic oxygen barrier, among other utilities. The mineral coatedmetal, with or without the secondary coating, can be used as a finishedproduct or a component to fabricate another article.

[0069] The thickness of the rinse, sealer and/or topcoat can range fromabout 0.00001 inch to about 0.025 inch. The selected thickness variesdepending upon the end use of the coated article. In the case ofarticles having close dimensional tolerances, e.g., threaded fasteners,normally the thickness is less than about 0.00005 inch.

[0070] Without wishing to be bound by any theory or explanation a silicacontaining layer can be formed. By silica it is meant a framework ofinterconnecting molecular silica such as SiO4 tetrahedra (e.g.,amorphous silica, cristabalite, triydmite, quartz, among othermorphologies depending upon the degree of crystalinity), monomeric orpolymeric species of silicon and oxide, monomeric or species of siliconand oxide embedding colloidal species, among others. The crystalinity ofthe silica can be modified and controlled depending upon the conditionsunder which the silica is deposited, e.g., temperature and pressure. Thesilica containing layer may comprise: 1) low porosity silica (e.g.,about 60 angstroms to 0.5 microns in thickness), 2) collodial silica(e.g., about 50 angstroms to 0.5 microns in thickness), 3) a mixturecomprising 1 and 2, 4) residual silicate such as sodium silicate and insome cases combined with 1 and 2; and 5) monomeric or polymeric speciesoptionally embedding other colloidal silica species such as colloidalsilica. The formation of a silica containing layer can be enhanced bythe addition of colloidal particles to the silicate medium. An exampleof suitable colloidal particles comprise colloidal silica having a sizeof at least about 12 nanometers to about 0.1 micron (e.g., Ludox® HS 40,AM 30, and CL). The colloidal silica can be stabilized by the presenceof metals such as sodium, aluminum/alumina, among others.

[0071] If desired, the silica containing film or layer can be providedin as a secondary process. That is, a first film or layer comprising adisilicate can be formed upon the metallic surface and then a silicacontaining film or layer is formed upon the disilicate surface. Anexample of this process is described in U.S. patent application Ser. No.60/354,565, filed on Feb. 05, 2002 and entitled “Method for TreatingMetallic Surfaces”; the disclosure of which is hereby incorporated byreference.

[0072] The silica containing layer can be chemically or physicallymodified and employed as an intermediate or tie-layer. The tie-layer canbe used to enhance bonding to paints, coatings, metals, glass, amongother materials contacting the tie-layer. This can be accomplished bybinding to the top silica containing layer one or more materials whichcontain alkyl, fluorine, vinyl, epoxy including two-part epoxy andpowder paint systems, silane, hydroxy, amino, mixtures thereof, amongother functionalities reactive to silica or silicon hydroxide.Alternatively, the silica containing layer can be removed by usingconventional cleaning methods, e.g, rinsing with de-ionized water, orone of the aforementioned post-treatments, e.g. acid rinsing. Ifdesired,. the silica containing layer can be chemically and/orphysically modified by employing the previously describedpost-treatments, e.g., exposure to at least one carbonate or acidsource. The post-treated surface can then be contacted with at least oneof the aforementioned secondary coatings, e.g; a heat cured epoxy.

[0073] In another aspect, the mineral without or without theaforementioned silica may layer functions as an intermediate ortie-layer for one or more secondary coatings, e.g., silane containingsecondary coatings. Examples of such secondary coatings and methods thatcan be complimentary to the instant invention are described in U.S. Pat.Nos. 5,759,629; 5,750,197; 5,539,031; 5,498,481; 5,478,655; 5,455,080;and 5,433,976. The disclosure of each of these U.S. Patents is herebyincorporated by reference. For example, improved corrosion resistance ofa metal substrate can be achieved by using a secondary coatingcomprising at least one suitable silane in combination with amineralized surface. Examples of suitable silanes comprise at least onemembers selected from the group consisting of tetraethylorthosilicate(TEOS) and TMOS with styrene, and etc., bis-1,2-(triethoxysilyl) ethane(BSTE), vinyl silane or aminopropyl silane, epoxy silanes,alkoxysilanes, methacryloxypropyl trimethoxysilanes, glycidoxypropyltrimethoxysilane, vinyltriactoxysilane, among other organo functionalsilanes. The silane can bond with the mineralized surface and then thesilane can cure thereby providing a protective top coat, or a surfacefor receiving an outer coating or layer. In some cases, it is desirableto sequentially apply the silanes. For example, a steel substrate, e.g.,a fastener, can be treated by the inventive process to form a minerallayer, allowed to dry, rinsed in deionized water, coated with a 5% BSTEsolution, coated again with a 5% vinyl silane solution, and powdercoated with a thermoset epoxy paint (Corvel 10-1002 by Morton) at athickness of 2 mils.

[0074] The inventive process forms a surface that has improved adhesionto outer coatings or layers, e.g., secondary coatings. Examples ofsuitable outer coatings comprise at least one member selected from thegroup consisting of acrylics, epoxies, e-coats, latex, urethanes,silanes (e.g., TEOS, TMEOS, among others), fluoropolymers, alkyds,silicones, polyesters, oils, gels, grease, among others. An example of asuitable epoxy comprises a coating supplied by The Magni® Group as B17or B18 top coats, e.g, a galvanized article that has been treated inaccordance with the inventive method and contacted with at least onesilane and/or ammonium zirconium carbonate and top coated with a heatcured epoxy (Magni® B18) thereby providing a chromate free corrosionresistant article. By selecting appropriate rinses, secondary and outercoatings for application upon the mineral, a corrosion resistant articlecan be obtained without chromating or phosphating. Such a selection canalso reduce usage of zinc to galvanize iron containing surfaces, e.g., asteel surface is mineralized, coated with a silane containing coatingand with an outer coating comprising an epoxy.

[0075] Without wishing to be bound by any theory or explanation, it isbelieved that the inventive process forms a surface that can release orprovide water or related moieties. These moieties can participate in ahydrolysis or condensation reaction that can occur when an overlyingrinse, seal or topcoating cures. Such participation improves thecohesive bond strength between the surface and overlying cured coating.

[0076] The surface formed by the inventive process can also be employedas an intermediate or tie-layer for glass coatings, glass to metalseals, hermetic sealing, among other applications wherein it isdesirable to have a joint or bond between a metallic substrate and aglass layer or article. The inventive surface can serve to receivemolten glass (e.g., borosilicate, aluminosilicate, phosphate, amongother glasses), while protecting the underlying metallic substrate andforming a seal.

[0077] The surface formed by the inventive process can also be employedas a heat resistant surface. The surface can be employed to protect anunderlying surface from exposure to molten metal (e.g., moltenaluminum).

[0078] The inventive process can provide a surface that improvesadhesion between a treated substrate and an adhesive. Examples ofadhesives comprise at least one member selected from the groupconsisting of hot melts such as at least one member selected from thegroup of polyamides, polyimides, butyls, acrylic modified compounds,maleic anhydride modified ethyl vinyl acetates, maleic anhydridemodified polyethylenes, hydroxyl terminated ethyl vinyl acetates,carboxyl terminated ethyl vinyl acetates, acid terpolymer ethyl vinylacetates, ethylene acrylates, single phase systems such as dicyanimidecure epoxies, polyamide cure systems, lewis acid cure systems,polysulfides, moisture cure urethanes, two phase systems such asepoxies, activated acrylates polysulfides, polyurethanes, among others.Two metal substrates having surfaces treated in accordance with theinventive process can be joined together by using an adhesive.Alternatively one substrate having the inventive surface can be adheredto another material, e.g., joining treated metals to plastics, ceramics,glass, among other surfaces. In one specific aspect, the substratecomprises an automotive hem joint wherein the adhesive is located withinthe hem.

[0079] The improved cohesive and adhesive characteristics between asurface formed by the inventive process and polymeric materials canpermit forming acoustical and mechanical dampeners, e.g., constraintlayer dampers such as described in U.S. Pat. No. 5,678,826 herebyincorporated by reference, motor mounts, bridge/building bearings, HVACsilencers, highway/airport sound barriers, among other articles. Theability to improve the bond between vistoelastomeric materialssandwiched between metal panels in dampers reduces sound transmission,improves formability of such panels, reduces process variability, amongother improvements. The metal panels can comprise any suitable metalsuch as 304 steel, stainless steel, aluminum, cold rolled steel, zincalloys, hot dipped zinc or electrogalvanized, among other materials.Examples of polymers that can be bonded to the inventive surface and inturn to an underlying metal substrate comprise any suitable materialsuch as neoprene, EPDM, SBR, EPDM, among others. The inventive surfacecan also provide elastomer to metal bonds described in U.S. Pat. No.5,942,333; hereby incorporated by reference.

[0080] The inventive process can employ dopants, rinses, sealers and/ortopcoats for providing a surface having improved thermal and wearresistance. Such surfaces can be employed in gears (e.g., transmission),powdered metal articles, exhaust systems including manifolds, metalflooring/grates, heating elements, among other applications wherein itis desirable to improve the resistance of metallic surfaces.

[0081] In another aspect of the invention, the inventive process can beused to produce a surface that reduces, if not eliminates, molten metaladhesion (e.g., by reducing intermetallic formation). Without wishing tobe bound by any theory or explanation, it is believed that the inventiveprocess provides an ablative and/or a reactive film or coating upon anarticle or a member that can interact or react with molten metal therebyreducing adhesion to the bulk article. For example, the inventiveprocess can provide an iron or a zinc silicate film or layer upon asubstrate in order to shield or isolate the substrate from molten fluidcontact (e.g., molten glass, aluminum, zinc or magnesium). Theeffectiveness of the film or layer can be improved by applying anadditional coating comprising silica (e.g., to function as an ablativewhen exposed to molten metal or glass). The ability to prevent moltenmetal adhesion is desirable when die casting aluminum or magnesium overzinc cores, die casting aluminum for electronic components, among otheruses. The molten metal adhesion can be reduced further by applying oneof the aforementioned topcoatings, e.g. Magni® B18, acrylics,polyesters, among others. The topcoatings can be modified (e.g., to bemore heat resistant, or reactive to alumina or aluminum) by adding aheat resistant material such as colloidal silica (e.g., Ludox®).

[0082] While the above description places particular emphasis uponforming a mineral containing layer upon a metal surface, the inventiveprocess can be combined with or replace conventional metal pre or posttreatment and/or finishing practices. Conventional post coating bakingmethods can be employed for modifying the physical characteristics ofthe mineral layer, remove water and/or hydrogen, among othermodifications. The inventive mineral layer can be employed to protect ametal finish from corrosion thereby replacing conventional phosphatingprocess, e.g., in the case of automotive metal finishing the inventiveprocess could be utilized instead of phosphates and chromates and priorto coating application e.g., E-Coat. The inventive process can beemployed for imparting enhanced corrosion resistance to electroniccomponents. The inventive process can also be employed in a virtuallyunlimited array of end-uses such as in conventional plating operationsas well as being adaptable to field service. For example, the inventivemineral containing coating can be employed to fabricate corrosionresistant metal products that conventionally utilize zinc as aprotective coating, e.g., automotive bodies and components, grain silos,bridges, among many other end-uses. Moreover, depending upon the dopantsand concentration thereof present in the mineral deposition solution,the inventive process can produce microelectronic films, e.g., on metalor conductive surfaces in order to impart enhanced electrical/magnetic(e.g., EMI shielding, reduced electrical connector fretting, reducecorrosion caused by dissimilar metal contact, among others), andcorrosion resistance, or to resist ultraviolet light and monotomicoxygen containing environments such as outer space.

[0083] The following Examples are provided to illustrate certain aspectsof the invention and it is understood that such an Example does notlimit the scope of the invention.

EXAMPLE 1

[0084] The effect on the deposit characteristics of the followingparameters were studied: (i) pH of bath, (ii) temperature of deposition,and (iii) rinsing immediately or after one day. Subsequent todeposition, impedance analysis and linear polarization were used toelectrochemically characterize the final deposit.

[0085] The base silicate medium solution comprised 800 mL of distilledwater+100 mL of PQ N Sodium Silicate solution (hereinafter referred toas 1:8 sodium: silicon solution). The PQ N Sodium Silicate solution is8.9 wt. % Na₂O and 28.7 wt. % SiO₂. The deposition was carried out in aplating cell made of glass on ACT zinc plated steel panels. Prior todeposition the panels were degreased with acetone and washed withdemineralized water. Two different sets of parameters were varied inthis experiment:

[0086] Firs th effect of pH was studied at 75° C. at 10.5, 10.8, 11,11.5 and 12.

[0087] Next, the effect of temperature was studied at 75° C., 80° C. and85° C.

[0088] For both studies, the immersion time was held constant at 15minutes. Subsequent to mineralization one set of panels was rinsedimmediately. The second set of samples were rinsed after 24 hours beforecarrying out the measurements.

[0089] Next, the corrosion characteristics of the panel were studied in0.5 M Na₂SO₄ solution at pH 4. A representative panel area of 1 cm² waschosen for testing. A three-electrode setup was used to study thecorrosion behavior of the mineralized samples. The electrolyte used inthis study is 0.5 M sodium sulfate, pH=4. Ti coated with Pd was used asthe counter electrode. Hg/Hg₂SO₄ was used as the reference electrode.All potentials in this study are referred with respect to the Hg/Hg₂SO₄electrode. Corrosion studies were done using Scribner AssociatesCorrware Software with EG&G Princeton applied Model 273potentiostat/galvanostat and a Solartron 1255 frequency analyzer inaccordance with conventional methods. The electrode was left on opencircuit till the potential is stabilized. After the potentialstabilized, non-destructive evaluation of the surface was done usinglinear polarization and impedance analysis. During linear polarization,the potential was varied 10 mV above and below the opencircuit-potential of the mineralized sample at a scan rate of 0.1667mV/s. The impedance data generally covered a frequency range of 5 mHz to10 kHz. A sinusoidal ac voltage signal varying by ±10 mV was applied.The electrode was stable during the experiments and its open circuitpotential changed less than 1 mV.

[0090] In moderately alkaline solutions (pH <10.5) zinc forms passivefilms which reduce the rate of metal dissolution. Increasing the pHabove 10.5 has a tendency to dissolve the passive film and active metalcorrosion. FIG. 1 presents the open-circuit potential of galvanized zincpanels immersed in the base solution of pH 10.5. As seen from the plot,the potential initially increases from an initial value of around −0.49V to more positive values. This indicates the formation of a passivefilm on the surface of zinc in presence of the base solution.

[0091]FIG. 2 shows the potential of galvanized steel in the basesolution, pH=11 as a function of time. As shown in FIG. 2, the potentialis more negative than that seen in FIG. 1 indicating formation of arelatively less stable film than the film formed at pH=10.5. However theobserved potential of −0.7 V vs Hg/HgO reference electrode stillindicates a passive film formation on Zn surface in presence of silicatesolution even at pH=11.

[0092] Increasing the pH further to 11.5, can reduce the effectivenessof the inventive process (see FIG. 3). Note that the corrosion potentialincreases up to −1.38 V vs Hg/HgSO₄ reference electrode which isdissolution potential for Zn.

[0093] According to Pourbaix (Pourbaix, M.: Atlas of ElectrochemicalEquilibria in Aqueous Solutions, 2nd ed., National Association ofCorrosion Engineers, Houston, pp. 406-413, 1974; hereby incorporated byreference), zinc exists in the various forms in solution, some of whichare given below. The various equilibrium reactions between the dissolvedsubstances are as follows: $\begin{matrix}{{{{Zn}^{2 +} + {H_{2}O}} = {{ZnOH}^{+} + H^{+}}};{{\log \quad \frac{\left( {ZnOH}^{+} \right)}{\left( {Zn}^{2 +} \right)}} = {{- 9.67} + {pH}}}} & (1) \\{{{{ZnOH}^{+} + {H_{2}O}} = {{HZnO}_{2}^{-} + {2H^{+}}}};{{\log \quad \frac{\left( {HZnO}_{2}^{-} \right)}{\left( {ZnOH}^{+} \right)}} = {{- 17.97} + {2\quad {pH}}}}} & (2) \\{{{{Zn}^{2 +} + {2H_{2}O}} = {{HZnO}_{2}^{-} + {3H^{+}}}};{{\log \quad \frac{\left( {HZnO}_{2}^{-} \right)}{\left( {Zn}^{2 +} \right)}} = {{- 27.63} + {3\quad {pH}}}}} & (3) \\{{{HZnO}_{2}^{-} = {{ZnO}_{2}^{-} + H^{+}}};{{\log \quad \frac{\left( {ZnO}_{2}^{-} \right)}{\left( {HZnO}_{2}^{-} \right)}} = {{- 13.11} + {pH}}}} & (4)\end{matrix}$

[0094] With the increase in pH, the equilibrium is shifted to the rightin all the above reactions. For reaction (2) and (3) the effect is morebecause of the greater dependence on H⁺ concentration. Between pH 8.98and 13.11 HZnO₂ ⁻ dominates. Beyond this ZnO₂ ⁻ is present.

[0095] This Example illustrate that increasing beyond a certain levelthe pH decreases the chances for the formation of a passive film.

[0096] At pH 12 (FIG. 4) corrosion increases and the metal potentialfluctuates significantly. Increasing the pH of the silicate mediumbeyond about 11 can cause active dissolution of the zinc leading todecreasing the protective zinc layer thickness. Increasing thetemperature is seen to accelerate the rate of metal dissolution. Similarbehavior is observed for pure Zn samples.

[0097]FIG. 5 and FIG. 6 summarizes the corrosion potentials determinedon galvanized steel samples in base solution at 75° and 80° C.,respectively. The corrosion potentials are shown as a function of timeestimated in solutions with pH 10.5, 11, 11.5 and 12. The resultsindicated that at pH 10.5 at 75° C. and 80° C. passive film forms whichis stable as a function of time. Note that increasing the temperaturefrom 75 to 80° C., the potentials estimated at pH=10.5 and 11 shifts forapproximately 200 mV in cathodic direction indicating a higherprobability for a decrease of the coating barrier properties.

[0098]FIG. 7 shows the open circuit potential studies for Zn platedsteel at different pHs (10.5, 11 and 12) in the absence of basesolutions. As expected the relatively high corrosion potentials (higherthan −1.0 V v. Hg/HgSO₄ reference electrode) were observed in theabsence of silica in the solution indicating a high probability for Zndissolution at pH 10.5 and higher

[0099] Tables 1 and 2 summarize the polarization resistance data ofsamples treated in accordance with the inventive mineralization processand tested at different temperatures and pH's (10.5, 10.8, 11, 11.5 and12). Subsequent to mineralization one set of panels was rinsedimmediately. The second set of samples was rinsed after 24 hours beforecarrying out the measurements. The rinsed panels data are presented inTable 1, while the data obtained from panels rinsed after 24 hours arepresented in Table 2. In general the samples rinsed after 24 hoursshowed higher resistances. Increase in temperature from 75° C. to 80° C.leads to an increase in resistance. In contrast increasing the pH from10.5 to 12 leads to a decrease in average resistance. TABLE 1 No CurrentData for temperatures 75, 80, and 85° C. - Rinse 0.5 M Na₂SO₄ pH 10.510.8 11 11.5 12 75° C. Rp (Ω) 586 2060 712 584 410 Rp (Ω) 697 1318 896595 422 Rp (Ω) 948 1429 686 183 404 Rp (Ω) 840 1231 609 801 473 Rp (Ω)858 799 916 609 Rp (Ω) 996 826 1441 931 Average 821 1510 755 753 542 80°C. Rp (Ω) 1072 1227 1219 849 731 Rp (Ω) 963 892 1252 719 710 Rp (Ω) 5401346 1526 830 778 Rp (Ω) 1319 2010 1301 624 905 Rp (Ω) 2203 1079 9751050 Rp (Ω) 3342 1951 998 898 Average 1573 1369 1388 833 845 85° C. 0.5M Na₂SO₄ pH 10.5 10.8 11 11.5 Rp (Ω) 249 1115 1887 783 Rp (Ω) 519 13232080 1268 Rp (Ω) 1078 1124 2133 1486 Rp (Ω) 1429 926 1603 1225 Rp (Ω)1855 Rp (Ω) 757 Rp (Ω) 586 Rp (Ω) 817 Average 819 1063 1926 1191

[0100] TABLE 2 No Current Data for temperatures 75, 80, and 85° C. -RINSED AFTER 24 HOURS 0.5 M Na₂SO₄ pH 10.5 10.8 11 11.5 12 75° C. Rp (Ω)1136 1757 1000 712 766 Rp (Ω) 846 1229 1295 727 592 Rp (Ω) 1223 16491327 641 950 Rp (Ω) 921 1423 983 1133 1044 Rp (Ω) 1458 4092 1624 1483 Rp(Ω) 3465 2509 2159 2106 Average 1508 1515 1868 1166 1157 80° C. Rp (Ω)793 983 1715 2564 804 Rp (Ω) 1490 989 1320 2809 931 Rp (Ω) 1418 10941874 2792 563 Rp (Ω) 1541 1085 1476 1973 509 Rp (Ω) 3565 2236 7370 982Rp (Ω) 1545 12413 1265 4904 Average 1725 1038 3506 3129 1449 85° C. 0.5M Na₂SO₄ pH 10.5 10.8 11 11.5 Rp (Ω) 785 729 941 1154 Rp (Ω) 810 1050883 1169 Rp (Ω) 638 1457 992 1041 Rp (Ω) 648 1577 7996 3769 Rp (Ω) 1197Rp (Ω) 519 Rp (Ω) 739 Rp (Ω) 957 Average 720 1028 2703 1783

EXAMPLE 2

[0101] A 1:8 (alkali to silica ratio) sodium silicate solution wasprepared as described in Example 1. The effect of deposition time, thepH of the silicate medium and the temperature of the silicate mediumwere studied. Prior to deposition the panels were degreased with acetoneand washed with demineralized water. The experiments were performed induplicate. One set of panels was rinsed immediately following depositionand a second set was rinsed 24 hours later. The corrosioncharacteristics of the panels were tested in 0.5 M Na₂SO₄ solution at pH4. A representative panel area of 1 cm² was tested. The rest of thepanel was masked with an insulating tape. A three-electrode setup wasused to study the corrosion behavior of the mineralized samples.Titanium coated with palladium was used as the counter electrode andHg/Hg₂Cl₂ was used as the reference electrode. All potentials are withrespect to the Saturated Calomel electrode. Corrosion studies were doneusing a Scribner Associates Corrware Software with EG&G PrincetonApplied Research Model 273 potentiostat/galvanostat and a Solartron 1255frequency analyzer in accordance with conventional procedures. Theelectrode was left on open circuit until the potential stabilized.Non-destructive evaluation of the surface was done using linearpolarization and impedance analysis. During linear polarization, thepotential was varied 10 mV above and below the open circuit potential ofthe mineralized sample at a scan rate of 0.1667 mV/s. The impedance datagenerally covered a frequency range of 5 mHz to 10 kHz. A sinusoidal ACvoltage signal varying by +/−10 mV was applied. The electrode was stableduring the experiments and its open circuit potential changed less than1 mV. Separately, samples were prepared for scanning electron microscopy(SEM) and EDAX analysis that were obtained by using a Hitachi S-2500Delta SEM.

[0102] Table 3 presents corrosion resistance data for electroless platedprepared at different bath temperatures. In general, increasing thetemperature from 25° C. to 75° C. leads to an increase in resistance.However, increasing the temperature further to 85° C. result in decreasein resistance. For these samples, 75° C. is a desirable bath temperaturefor electroless mineralization. TABLE 3 Comparison of corrosionresistance for samples mineralized at different bath temperatures.Resistance (Ω-cm²) in pH 4, 0.5 M Na₂SO₄ Temperature 25° C. 75° C. 85°C. Loca- Immediate 24 Hour Immediate 24 Hour Immediate 24 Hour tionRinse Rinse Rinse Rinse Rinse Rinse 1 301 216 586 1136 249 718 2 225 321697 846 519 835 3 265 345 948 1223 1078 638 4 400 425 840 921 1429 648 5350 500 858 1458 819 720 6 215 322 996 3465 534 810 Avg. 292.7 354.8 8211508 771.3 728.2 High 400 500 996 3465 1429 835 Low 215 216 586 846 519638

[0103] Table 4 presents corrosion resistance data for electroless platedsamples prepared at pH 10.5 and 11. Increasing the pH from 10.5 to 11leads to an increase in average resistance. Samples that are rinsedafter 24 hours typically exhibit better corrosion resistance thansamples rinsed immediately. The same trend is observed for the samplesprepared at different temperatures. FIG. 8 shows a comparison of the SEMand EDAX analysis of samples rinsed immediately and rinsed after 24hours. Samples rinsed immediately have no detectable Si on the surfacewhereas samples rinsed after 24 hours shows 12% Si on the surface. Thiscorresponds to the increased resistance shown in Table 3 and 4. TABLE 4Comparison of corrosion resistance for samples mineralized at differentpH in 1:8 sodium silicate at 75° C. Resistance (Ω-cm²) in pH 4, 0.5 MNa₂SO₄ 10.5 11 pH Immediate 24 Hour Immediate 24 Hour Location RinseRinse Rinse Rinse 1 586 1136 712 1000 2 697 846 896 1295 3 948 1223 6861327 4 840 921 609 983 5 858 1458 799 4092 6 996 3465 826 2509 Avg. 8211508 755 1868 High 996 3465 896 4092 Low 586 846 609 983

[0104] Table 5 presents compares the corrosion resistance of sampleswith different deposition times. In general, the resistance ranges from1400-1700 W-cm2. TABLE 5 Corrosion Resistance for samples mineralized in1:8 sodium silicate at 75° C. at different deposition times. Resistance(Ω-cm²) in pH 4, 0.5 M Na₂SO₄ Location 5 minutes 10 minutes 15 minutes20 minutes 1 2500 1885 2412 759 2 754 684 867 2295 3 913 2286 1686 1959Avg. 1389 1618.3 1655 1668 High 2500 2286 2412 2295 Low 754 684 867 759

[0105] In view of the above data presented in Example 1 and 2, one ofskilled in the art should understand and appreciate that themineralization bath should be heated, typically to a temperature ofabout 70 to 80 C. One should also note that in general, rinsing thesamples 4 hours after mineralization results in increased resistancemeasurements and higher silicon content than samples immediately rinsedafter treatment. Finally it should be noted by a skilled artisan, thatthe corrosion resistance of the sample verse time is optimized afterapproximately 15 minutes of treatment in the mineralization bath. Thetemperature of the bath, silicate concentration and drying regime can beemployed for optimizing the corrosion resistance of the treated metalsurface.

EXAMPLE 3

[0106] As shown above, samples that are rinsed after 24 hours can showincreased resistance compared to samples that are rinsed immediately,suggesting that the silicate dries and crystallizes on the surface. Thepresent example demonstrates (i) the effect of post-mineralizationheating and (ii) the effect of the concentration of the silicate bath.

[0107] A first set of samples were mineralized in a 1:8 (alkali:silicaratio) silicate solution for 15 minutes and dried at 100° C. for onehour immediately. A second set was mineralized and left to dry at roomtemperature for 24 hours. Table 6 shows corrosion resistance for thesamples. Heating results in a dramatic increase in corrosion resistance,but the resistance may not be uniform across the samples, indicatingnon-uniformity of Si on the surface. TABLE 6 Comparison of resistancefor samples mineralized in 1:8 sodium silicate with and withoutpost-deposition heating. Resistance (Ω-cm²) in pH 4, 0.5 M Na₂SO₄Heating at 100° C. Location No Heating for 1 hour 1 2412 4.4 × 10⁴ 2 8674.7 × 10⁴ 3 1686 725.2 Avg. 1655 3.1 × 10⁴ High 2412 4.7 × 10⁴ Low 867725.2

[0108] Table 7 shows the corrosion resistance of samples mineralized asabove and heated at different temperatures for one hour. Increasing thedrying temperature typically increases the average resistance. TABLE 7Comparison of resistance for samples mineralized in 1:8 sodium silicateand heated at different post-deposition temperatures. Resistance (Ω-cm²)in pH 4, 0.5 M Na₂SO₄. Location 100° C. 125° C. 150° C. 175° C. 200° C.1 4.4 × 10⁴ 702.9 8.2 × 10⁴ 1.2 × 10⁵ 2.1 × 10⁵ 2 4.7 × 10⁴ 6.8 × 10⁴8.4 × 10⁴ 1600 780.7 3 725.2 4.0 × 10⁴ 1644.3 8.2 × 10⁴ 2.3 × 10⁴ Avg.3.1 × 10⁴ 3.5 × 10⁴ 5.6 × 10⁴ 6.8 × 10⁴ 7.8 × 10⁴ High 4.7 × 10⁴ 6.8 ×10⁴ 8.4 × 10⁴ 1.2 × 10⁵ 2.1 × 10⁵ Low 725.2 702.9 1644.3 1600 780.7

[0109] The samples of Table 8 were placed under water for seven days,and the corrosion resistance determined periodically. As shown in Table8, the resistance drops to less than 1000 Ω-cm² for all the samplesafter seven days. Without wishing to be bound by any theory ofexplanation it is believed that water can penetrate through microcracksin the coating and attacks the underlying layer. The dissolution of Zncan lead to the removal of the protective coating and eventually causesthe corrosion rate to increase. TABLE 8 Comparison of resistance after 1week immersed in water for surfaces mineralized in 1:8 sodium silicate.Resistance (Ω-cm²) in pH 4, 0.5 M Na₂SO₄. No. of days 100° C. 125° C.150° C. 175° C. 200° C. Initial 3.1 × 10⁴ 3.6 × 10⁴ 6.0 × 10⁴ 6.5 × 10⁴8.1 × 10⁴ 1 day 822.8 844.1 1240.5 1521.6 1623.5 4 days 580.1 612.5800.2 911.3 954 7 days 400.1 512.3 564.7 603.1 625.4

[0110] Table 9 presents corrosion resistance data for samplesmineralized in different concentrations of silicate solution. In thisexample, a series of bath solutions having differing ratios of PQsolution to water were prepared. For example, a 1:1 solution wasprepared by adding 1 part PQ solution to 1 part water. Followingmineralization, the samples were heated at 100° C. for 1 hour. Datarepresentative of the results achieved are given below. One of skill inthe art should understand and appreciate that the corrosion resistancegenerally increases with bath concentration. With the 1:8 and the 1:4baths, the corrosion resistance appears to be variable across thesurface. However, with the 1:3 ratio bath and higher ratio baths,resistances in the range of 10⁵ Ω-cm² are measured across the surface.Thus one of skill in the art should conclude that the 1:3 is a desirablebath concentration for these samples. TABLE 9 Comparison of resistancefor surfaces mineralized in different concentrations of sodium silicatesolution. Resistance (Ω-cm²) in pH 4, 0.5 M Na₂SO₄ Location 1:8 1:4 1:31:2 1:1 1 4.4 × 10⁴ 8200 3.3 × 10⁵ 7.7 × 10⁵ 2.2 × 10⁶ 2 4.7 × 10⁴ 1.7 ×10⁵ 1.8 × 10⁵ 1.2 × 10⁶ 1.8 × 10⁶ 3 725.2 3.0 × 10⁵ 4.9 × 10⁵ 1.3 × 10⁶1.9 × 10⁶ Avg. 3.1 × 10⁴ 6.9 × 10⁴ 3.3 × 10⁵ 1.1 × 10⁶ 2.0 × 10⁶ High4.7 × 10⁴ 3.0 × 10⁵ 4.9 × 10⁵ 1.3 × 10⁶ 2.2 × 10⁶ Low 725.2 8200 1.8 ×10⁵ 7.7 × 10⁵ 1.8 × 10⁶

[0111] Samples mineralized in 1:3 sodium silicate were heated atdifferent temperatures for 1 and kept under water for seven days. Asshown in Table 10, the resistances measured immediately after drying,indicate that increasing drying temperature tends to increase theaverage resistance of the samples. However, the resistances of all thesample can drop to under 1000 W-cm2 after seven days immersed in water.TABLE 10 Comparison of resistance after 1 week immersed in water forsurfaces mineralized in 1:3 sodium silicate and heated at varioustemperatures for 1 hour. Resistance (Ω-cm²) in pH 4, 0.5 M Na₂SO₄.Location Room temp. 100° C. 125° C. 150° C. 175° C. 200° C. 1 2246 3.3 ×10⁵ 7.1 × 10⁵ 7.2 × 10⁵ 3.2 × 10⁵ 8.0 × 10⁵ 2 1879 1.8 × 10⁵ 6.8 × 10⁵8.4 × 10⁵ 1.2 × 10⁶ 1.5 × 10⁶ 3 2224 4.9 × 10⁵ 1.4 × 10⁵ 4.8 × 10⁵ 9.2 ×10⁵ 1.0 × 10⁶ Avg. 2116.2 3.3 × 10⁵ 5.1 × 10⁵ 6.8 × 10⁵ 8.1 × 10⁵ 1.1 ×10⁶ High 2246 4.9 × 10⁵ 7.8 × 10⁵ 8.4 × 10⁵ 1.2 × 10⁶ 1.5 × 10⁶ Low 18791.8 × 10⁵ 1.4 × 10⁵ 4.8 × 10⁵ 3.2 × 10⁵ 8.0 × 10⁵

[0112] TABLE 11 Comparison of resistance after immersion in water forsurfaces mineralized in 1:3 sodium silicate and heated at varioustemperatures for 1 hour. Resistance (Ω-cm²) in pH 4, 0.5 M Na₂SO₄. DaysRoom temp. 100° C. 125° C. 150° C. 175° C. 200° C. Initial 2116.2 3.5 ×10⁵ 5.0 × 10⁵ 6.8 × 10⁵ 8.4 × 10⁵ 1.3 × 10⁶ 1 632.1 2247.8 2509 2496.23561.3 3626 4 601.1 1028.2 978 856.3 1211.3 1490.4 7 580 532.1 612.3632.6 657.7 691.9

[0113] The dried samples can be rinsed to remove any water solublespecies. If desired, the rinse solution .can comprise at least onecomposition for further modifying the dried sample (e.g., silanes,colloidal silica, among other materials).

EXAMPLE 4

[0114] Hydrogen is evolved at the surface of the cathode duringelectroplating and the rate of hydrogen evolution can be controlled byvarying the applied potential or current. Hydrogen production alsoreleases hydroxyl groups into the solution thereby increasing pH.However, in the case of electroless deposition, this can be accomplishedthrough the use of selected reducing agents.

[0115]FIG. 9 presents the Si concentration of samples mineralized in1500 mL of 1:3 sodium silicate in the presence of increasing amounts ofsodium borohydride. Comparison of the samples dried in air with thesamples heated at 175 C is shown. With samples dried in air, the Sicontent increases with borohydride concentration. With the heatedsamples, the Si content initially decreases with borohydrideconcentration, but no decrease is observed at borohydride concentrationsgreater than 5 g.

[0116] The stability of the coatings prepared without post-depositionheating is shown in Table 12 (note as shown above post-depositionheating improves corrosion resistance). The stability of the coatings isimproved by the addition of sodium borohydride. The corrosion resistanceof the coatings prepared with 10 g of sodium borohydride drops from1941.5 W-cm2 to 1372.1 W-cm2 after seven days, whereas the resistance ofcoating prepared in the absence of sodium borohydride drops from 2116.2W-cm2 to 580 W-cm2. FIG. 10 shows a plot of this data. TABLE 12Comparison of resistance after immersion in water for surfacesmineralized in 1500 mL of 1:3 sodium silicate in the presence of variousamounts of sodium borohydride. Resistance (Ω-cm²) in pH 4, 0.5 M Na₂SO₄.Days immersion No NaBH₄ 5 g NaBH₄ 10 g NaBH₄ 15 g NaBH₄ Initial 2116.21870.1 1941.5 2168.9 1 632.1 1650.7 1660.2 2071.7 4 601.1 1072.1 1491.81856.2 7 580 830.1 1372.1 1590.1

[0117] A similar trend is observed with samples subjected topost-mineralization heating at 175° C. for one hour. The averageresistance of the coating prepared using 10 g of sodium borohydridedrops to 1488.6 W-cm2 after seven days, compared to 570.7 W-cm2 observedafter seven days for the coating prepared in the absence of sodiumborohydride (Table 13). A plot of this data is shown in FIG. 11. TABLE13 Comparison of resistance after immersion in water for surfacesmineralized in 1500 mL of 1:3 sodium silicate in the presence of variousamounts of sodium borohydride and heated at 175° C. for one hour.Resistance (Ω-cm²) in pH 4, 0.5 M Na₂SO₄ Days immersion No NaBH₄ 5 gNaBH₄ 10 g NaBH₄ 15 g NaBH₄ Initial 3.3 × 10⁵ 4.1 × 10⁴ 1.9 × 10⁴ 3456 11690.4 1488.6 2677.8 2131.2 4 983.1 1132.4 1939.0 1446.7 7 570.7 916.11488.6 1243.1

[0118] Surfaces mineralized in 1500 mL of 1:3 sodium silicate in thepresence of different amounts of sodium borohydride were used as workingelectrodes for cyclic voltammetry in a three electrode cell, using acalomel reference electrode and a scan rate of 5 mV/s. One set ofsurfaces was dried in air for 24 hours, while a second set was heated at175° C. for one hour. FIG. 12 shows voltamograms for the air driedsamples. The observed current corresponds to corrosion of the surfacelayer. At a bare galvanized surface, increasing the potential morepositive than −1.1 V leads to stripping Zn from the surface. In thereverse scan, deposition is observed as mass transfer limited current.

[0119] For the SiO₂-coated surfaces, peak reduction current and maximumoxidation current can decrease rapidly. Since the currents are dependentof the amount of material lost from the surface, the inhibitingefficiency of the silica on Zn can be estimated from the voltammogramsas:

[0120] Inhibiting efficiency (%)=[(Peak Current Coated)/(Peak CurrentBare)]×100

[0121]FIG. 13 shows a plot of the inhibiting efficiencies from thevoltammogram of FIG. 12. The inhibiting efficiency typically increaseswith increasing sodium borohydride concentration.

[0122] Voltammograms of the surfaces coated in the presence of sodiumborohydride and heated at 175° C. for one hour are shown in FIG. 14.Currents in the SiO₂-coated samples are negligible compared to the baresurface. The inhibiting efficiency is shown in FIG. 15.

[0123] Cyclic voltammetry (CV) was performed with surfaces with andwithout post-mineralization heating after immersing them in water forone week. FIG. 16 shows the CVs of the samples prepared in the presenceof different amounts of sodium borohydride and air-dried for 24 hours.The current increases to the order of 1 mA after one week. FIG. 17 showsthe decrease in the inhibiting efficiency after one week immersion inwater. Similar results are observed for the surfaces subjected topost-deposition heating at 175° C. for one hour (FIGS. 18 and 19). Thechange in inhibiting efficiency is the lowest for samples prepared with10 g of sodium borohydride.

[0124]FIG. 20 shows SEM images of surfaces prepared in the presence of10 g of sodium borohydride before and after immersion in water. Uponinspection one of skill in the art should notice that a 2 μm crack isobserved. It will be appreciated by such a skilled artisan that suchcracks facilitate the entry of water through the coating and allowattack of the underlying surface. As the cracks become large, to theorder of 8-10 mm and flakes of zinc appear on the surface. EDAX onsurfaces coated in the presence of different amounts of sodiumborohydride and left to dry in air for 24 hours indicates that the Sicontent drops for all the samples, but the drop is the least for thesample prepared in the presence of 10 g of sodium borohydride (FIG. 21).Similar behavior is observed for surfaces prepared with post-depositionheating (FIG. 22).

[0125] These studies indicate to one of skill in the art that surfacescoated via electroless mineralization in the presence of sodiumborohydride.

EXAMPLE 5

[0126] The following table shows examples of the inventive process thatemploys a heated silicate medium for treating standard M-10 bolts. Theheated silicate medium comprised 10% N-Grade PQ sodium silicate solution(which comprises 2.88% SiO2, 0.90% alkali) and silica colloids thatranged in size from about 10 nm to about 1.000 nanometers (and typically1 to 100 nm). STANDARD M-10 BOLT RUN PARAMETER SUMMARIES Bath Number OfTotal Bolt D.C. D.C. Run # Time (Min) Temp (C) CD (ASI) A:C Area BoltsArea (sq. ln) Current (A) Potential (V) Results 1 15 74.3-75.8 0.0551-1.9 100 500 28 10.7-15.0 Bright & Silvery Appearance 2 0 N/A 0 0 100500 0 0 Eclipse Zinc Plate Control 3 0 N/A 0 0 100 500 0 0 Eclipse ZincPlate Control 4 15 74.6-75.5 0.055 1:1.9 100 500 27.5 10.9-12.3 Bright &Silvery Appearance 5 15 71.3-74.5 0 0 100 500 0 0 Hot Soak 6 1572.8-75.1 0 0 100 500 0 0 Hot Soak 7 0 N/A 0 0 100 500 0 0 Eclipse ZincSupplied by Atotech ® 8 0 N/A 0 0 100 500 0 0 Eclipse Zinc Supplied byAtotech ® 9 15 36.3-37.1 0 0 68 340 0 0 Cold Soak 10 15 74.5-75.6 0 0 22110 0 0 Hot Soak 1 0 N/A 0 0 6 30 0 0 Zinc Plate Control 2 15 26.6 0 023 115 0 0 Cold Soak 3 15 74.3-75.6 0 0 24 120 0 0 Hot Soak 4 2.573.1-74.9 0.1 1:1   53 265 27 <24.7 Bright & Silvery Appearance 5 1524.6 0 0 9 45 0 0 Cold Soak/New Solution 6 15 73-75 0 0 9 45 0 0 HotSoak/New Solution 7 15 74.5-75.2 0 0 6 30 0 0 Hot Soak

[0127] POST-TREATMENT/TOPCOATS Group # Run# Post-Treat. Top-Coat  1A 2Dry Only None  1B 3 Dry Only None 2 3 Dry Only Magni ® B17 3 2 Dry OnlyMagni ® B18  4A 5 A Process None  4B 6 A Process None 5 6 A ProcessMagni ® B17 6 5 A Process Magni ® B18  7A 1 A Process None  7B 4 AProcess None 8 4 A Process Magni ® B17 9 1 A Process Magni ® B18 10 7/8Corrosil None 11 7/8 Corrosil Magni ® B17 12 7/8 Corrosil Magni ® B18 137/8 Ecotri None 14 7/8 Ecotri Magni ® B17 15 7/8 Ecotri Magni ® B18 16 9Dry Only None 17 9 A Process None 18 9 A Process Magni ® B17 19 9 AProcess Magni ® B18 20 10 A Process None 1 1 Dry Only None 2 2 Dry,Rinse, Dry None 3 3 Dry, Rinse, Dry None 4 4 Dry, Rinse, Dry None 5 5Immediate Rinse None New Solution: 6 5 Dry, Rinse, Dry None NewSolution: 7 6 Immediate Rinse None New Solution: 8 6 Dry, Rinse, DryNone New Solution: 9 7 Spin Dry Only None Ripened Solution 10 6 Spin DryOnly None New Solution:

[0128] Upon review of the above representative data and information, oneof skill in the art should understand and appreciate that the process ofthe present invention can be carried out in a routine manner onindustrial parts and workpieces using standard metal finishingequipment. It should also be appreciated that the mineralized samplescan be further treated with a top coat or other additional protectivecoating to aid in the handling and transport of the mineralized parts orworkpieces.

EXAMPLE 6

[0129] The present example illustrates the effect of post-treatmentheating of the samples. The edge of a 2.75 inch diameter×6 inch longelectric motor laminate core assembly comprising individual laminates(high silicon steel alloy) mechanically coined together and assembledonto a simulated shaft was treated. These laminates can be used fromconstructing the rotor of an electric motor. Mineralization was carriedout in a 1:3 ratio bath made of 1 part sodium silicate (PQ) solution and3 parts water. The temperature of the bath was maintained at 75 C and adeposition time of 15 minutes. Post treatment heating of the samples wascarried out at 25 C until the sample was dry and 175 C until the samplewas dry.

[0130] Data representative of the corrosion resistance (Ω-cm²) in pH 4,0.5 M Na₂SO₄ Solution of the samples mineralized in a 1:3 PQ Bath at pH10.5 for 15 minutes is given below Location 25 C. dry 120 C. dry 11087.8 38146 2 2222.1 61923 3 1600 48083 Average Value 1636.6 49384

[0131] Data representative of the corrosion resistance (Ω-cm²) in pH 4,0.5 M Na₂SO₄ Solution of the samples mineralized in Mineralize in 1:3 PQBath with NaBH₄ (10 g/l), at pH 10.5 for 15 minutes is given belowLocation 25 C. dry 120 C. dry 1 6883.2 26961 2 15108 27049 3 7711.424858 Average Value 9900.9 26289

[0132] EDAX analysis of the samples dried at 25 C and prepared in theNaBH4 containing bath is compared to the samples prepared without theNaBH4 gave the following exemplary data: NaBE₄ Control Bath (no NaBH₄)Atomic % Oxygen 0.000 0.000 Silicon 55.187 42.329 Iron 44..813 57.671Conc. (Wt %) Oxygen 0.00 0.000 Silicon 38.247 26.960 Iron 61.753 73.040

[0133] Upon review of the above exemplary data, one of skill in the artshould understand and appreciate that the inclusion of NaBH4 into themineralization bath substantially increases the mineralized protectivelayer formed.

[0134] Examples 7-9 illustrate silicate media containing complexingagents and dopants. These silicate media were prepared in laboratoryscale equipment.

EXAMPLE 7

[0135] 20 gms of sodium citrate dihydrate (complexing agent), 1 gmNickel chloride (dopant), 1 gm Molybdenum (dopant), and 1 gm cobaltchloride (dopant) were dissolved in 500 ml of water to prepare a firstsolution. Then and 0.5 gm of MgO and 1 gm aluminum dissolved in 1:3sodium silicate solution (supplied by PQ) which when added to the 500 mlwater makes up 1:3 bath to prepare a second solution. The first andsecond solutions were combined. The combined solution had a violet hueand pH of about 11.5.

EXAMPLE 8

[0136] 20 gms of sodium citrate dihydrate, 1 gm nickel chloride, 1 gmcobalt chloride, and 0.5 gm molybdenum were dissolved in 500 ml of waterin order to prepare a first solution. Then a second solution of 1:3sodium silicate was prepared. The first and second solutions werecombined. The combined solutions had a violet hue and pH of about 11.0.

EXAMPLE 9

[0137] 20 gms of Sodium citrate dihydrate, 1 gm Nickel chloride, 0.5 gmMolybdenum, and 1 gm cobalt chloride were dissolved in 500 ml of waterin order to prepare a first solution. A second solution comprising 1:3sodium silicate was prepared. The first and second solutions werecombined.

[0138] If desired a reducing agent solution comprising sodiumborohydride (e.g., 4 grams of sodium borohydride dissolved in 50 mlwater) can be added to solutions of Examples 7-9.

[0139] While the apparatus, compositions and methods of this inventionhave been described in terms of preferred or illustrative embodiments,it will be apparent to those of skill in the art that variations may beapplied to the process described herein without departing from theconcept and scope of the invention. All such similar substitutes andmodifications apparent to those skilled in the art are deemed to bewithin the scope and concept of the invention.

The following is claimed:
 1. An electroless method for treating asubstrate having an electrically conductive surface comprising:contacting at least a portion of the surface with a medium comprising atleast one silicate and having a basic pH and wherein said medium issubstantially free of chromates, drying the substrate, rinsing thesubstrate, drying the substrate.
 2. An aqueous medium for use in anelectroless process for treating a conductive surface comprising acombination comprising water, at least one water soluble silicate,colloidal silica, at least one dopant and wherein the medium has a basicpH and is substantially free of chromates and VOCs.
 3. An electrolessmethod for treating a metallic or an electrically conductive surfacecomprising: exposing at least a portion of the surface to a mediumcomprising a combination comprising water, colloidal silica, and atleast one water soluble silicate wherein said medium has a basic pH,drying the surface, rinsing the surface, drying the surface; andcontacting the treated surface with at least one composition thatadheres to the treated surface.
 4. The method of claim 1 wherein themedium comprises water, sodium silicate and colloidal silica.
 5. Themethod of claim 1 wherein the surface comprises at least one memberselected from the group consisting of copper, nickel, tin, iron, zinc,aluminum, magnesium, stainless steel and steel and alloys thereof. 6.The method of claim 1 wherein said rinsing comprises contacting thesurface with a second medium comprising a combination comprising waterand at least one water soluble compound selected from the groupconsisting of carbonates, chlorides, fluorides, nitrates, zironates,titanates, sulphates, water soluble lithium compounds and silanes. 7.The method of claim 1 wherein the medium comprises at least one dopantselected from the group consisting of zinc, cobalt, molybdenum andnickel.
 8. The method of claim 1 wherein said first drying is conductedat a temperature of at least about 120C.
 9. The method of claim 1further comprising applying at least one coating upon the surface. 10.The medium of claim 2 wherein the medium comprises a combinationcomprising water, colloidal silica, greater than 1 wt. % of sodiumsilicate and further comprises at least one dopant selected from thegroup consisting of cobalt, nickel, molybdenum and zinc.
 11. The methodof claim 1 further comprising forming a layer comprising silica upon thesurface.
 12. The medium of claim 3 wherein said dopant comprises atleast one member selected from the group consisting of from the group oftitanium chloride, tin chloride, zirconium acetate, zirconiumoxychloride, calcium fluoride, tin fluoride, titanium fluoride,zirconium fluoride; ammonium fluorosilicate, aluminum nitrate; magnesiumsulphate, sodium sulphate, zinc sulphate, copper sulphate; lithiumacetate, lithium bicarbonate, lithium citrate, lithium metaborate,lithium vanadate and lithium tungstate.
 13. The method of claim 1wherein said medium comprises sodium silicate, water, colloidal silicaand at least one dopant, said rinsing is conducted with a second mediumcomprising water and at least one member selected from the groupconsisting of silanes and colloidal silica and further comprisingapplying at least one secondary coating comprising at least one memberselected from the group consisting of acrylics, urethanes, polyester andepoxies.
 14. The method of claim 1 wherein said rinsing comprisingcontacting said surface with a solution comprising water and at leastone dopant.
 15. The method of claim 14 wherein the dopant comprises atleast one member selected from the group consisting of molybdenum,chromium, titanium, zircon, vanadium, phosphorus, aluminum, iron, boron,bismuth, gallium, tellurium, germanium, antimony, niobium, magnesium,manganese, zinc, aluminum, cobalt, nickel and their oxides and salts.16. The method of claim 3 further comprising prior to said exposingcontacting said surface with a pretreatment comprising at least onemember selected from the group consisting of acid and basic cleaners.17. The method of claim 1 wherein said medium further comprises at leastone dopant.
 18. The method of claim 3 wherein said adherent compositioncomprises at least one member chosen from the group of latex, silanes,epoxies, silicone, amines, alkyds, urethanes, polyester and acrylics.